A method for operating a fuel injector is described in German Patent Application No. DE 10 2012 206 586 A1. The fuel injector has at least one injection orifice which is controlled by an injector needle, and a control space for the injector needle, which communicates with a high-pressure side and a low-pressure side of the fuel injector; using a control-valve system, a closing pressure at which the injector needle is positioned in a closing position that seals the injection orifice, and an opening pressure, at which the injector needle transitions into an open position that releases the injection orifice, are adjustable in the control space, and pressure changes during the opening and/or closing of the injector needle are ascertained with the aid of a sensor.
In order to provide a precise control of the injection quantity of such a fuel injector in a manner that requires limited resources, a dynamic pressure in the fuel injector is sensed with the aid of the sensor, which preferably is a force and/or pressure sensor. Utilizing such a pressure sensor, which is normally developed as a piezo sensor or a resistance strain gauge (RSG), the pressure in the high-pressure bore is measured and recorded so that an opening or closing operation of the needle may be detected. The signal curve is used to ascertain the instants for the opening and/or closing of the injector needle or the valve. The time between the event of the opening/closing of the injector needle or the valve and its detection is now a function of the propagation time of a pressure wave from the event to the sensor. This wave propagation time is in turn dependent upon the temperature, the pressure of the fuel and the fuel type, for instance. Small delay times in the detection of the opening/closing operation may make a control on that basis imprecise, which could have a detrimental effect on the operation of the internal combustion engine and especially its emissions.
Therefore, it is desired to ensure a chronologically correct detection even if the wave propagation time varies, e.g., on account of the pressure, the temperature or the type of fuel.